Aerobic fermentation is a sustainable option for livestock waste treatment, but little is known about the microbial mechanism that allows oxytetracycline (OTC) and copper (Cu) to affect nitrogen metabolism during aerobic fermentation. In this study, contamination with OTC and Cu alone or in combination reduced the total nitrogen (TN) content of the fermentation products. Metagenomic analysis demonstrated that the contribution of microorganisms to nitrogen metabolism changed significantly in different stages of fermentation. OTC and Cu affected the formation and utilization pattern of NO2--N by microorganisms, which were mainly responsible for the reduced N2O emissions. In the presence of OTC and/or Cu, Myxococcus_stipitatus, Myxococcus_xanthus, and Gimesia_maris were evidently enriched at the end of fermentation, and their increased roles in the dissimilatory reduction of nitrite to ammonium were confirmed by network analysis. Ardenticatena_maritima was the main contributor to denitrification (NO3--N to NO). Furthermore, organic matter (OM) was the most important factor responsible for driving the variation in nitrogen-transforming microorganisms and controlling denitrification. OTC affected the formation of OM, which can directly affect TN (λ = -0.37, p < 0.001), and the adverse impact of Cu on nirK- and nifH-dominant microorganisms was validated (p < 0.05).
Keywords: Agricultural waste; Assimilation and dissimilation of nitrite reduction; Functional genes; Metagenomics; Nitrogen preservation.
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